[3DDesign]

Drive a ground rod about 50 ft away and run an insulated wire, like #12 THHN back to the area. Start testing for voltage using the rod as ground.
I found voltage leaking from a POCO sub-station like that once.
Another time I found the entire industrial building had 120V on the metal frame.

 

[3DDesign]

I wired a Hot Tub. While in the tub, you could feel a trickle of electricity when you touched the concrete around it, about 2 or 3 volts. I finally proved to the POCO that their sub-station about 1,000 ft away was leaking voltage into the ground.
As I neared the sub station, I could get 10V by sticking the meter's leads into the ground 6ft apart.

 

[3DDesign]

Did they say what they’re going to do about it?

They denied it for weeks. Finally I got an Engineer out there and showed him my test with a ground driven 200ft away and an insulated conductor to measure from.
They fixed it after that.